The present invention relates to controlling vanes having a variable setting angle. A particular application for the invention lies in the field of aviation, in particular for controlling the angular positions of air inlet guide vanes in the compressors of turbomachines, such as airplane turbomachines.
Known devices for controlling variable-setting vanes in a turbomachine generally comprise a control member in the form of a ring surrounding the casing of the turbomachine and a plurality of levers or links, each link having a first end connected to the control ring via a hinge and a second end mounted on the pivot of a respective vane.
The angular position of the vanes is changed synchronously by turning the ring about the axis of the turbomachine. In order to be able to follow the turning movement of the ring, the connection between each link and the ring has at least one degree of freedom in rotation about an axis extending substantially radially relative to the ring. Nevertheless, since the link is rigidly mounted to the pivot of the corresponding vane, turning the ring induces other relative movements between the ring and the portion of the link mounted on the vane pivot. In order to accommodate these additional movements, or at least some of them, it is known to make the connection in the form of a ball-and-socket joint or an analogous part which, in addition to turning about an axis that is substantially radial relative to the ring, also allows turning to take place about an axis that is substantially circumferential in direction relative to the ring. Proposals have also been made for a connection that offers an additional degree of freedom in translation in a direction that is substantially radial relative to the ring. Reference can be made to documents FR-A-2 608 678 or FR-A-2 746 141, amongst others.
U.S. Pat. No. 6,019,574 discloses a mechanical hinge between the vane pivot and the end of the link mounted thereon by means of a tenon-and-mortise system: the vane pivot has a threaded end passing through an orifice pierced through the control link. A nut tightened onto the threaded end of the pivot enables this assembly of parts to turn together. Similarly, in European patent application EP 1 010 862 a hinge is described that is obtained by drive studs secured to the vane pivot and penetrating into slots formed at the end of the link mounted on the pivot. That assembly is likewise caused to rotate as a whole by means of a nut screwed onto a threaded end of the vane pivot.
Nevertheless, in those documents, the precision with which the control link turns relatively to the vane pivot leaves an error in the range 0.4xc2x0 to 0.6xc2x0 in common practice. This low level of precision stems from the fact that clearance exists between the various parts due to the assembly tolerances of the control device. Slack occurs in particular between the pivot and the end of the link mounted thereon. This gives rise to lack of precision in turning the link which is particularly harmful to proper operation of the assembly.
The present invention thus seeks to mitigate such drawbacks by proposing a control device using fixing means for the link which enable it to be held without slack on the vane pivot. Another object of the invention is to eliminate lack of precision in turning.
To this end, the invention provides a device for controlling a variable-angle vane for a stator of a turbomachine compressor, the device comprising a link, connection means forming a hinge between a first end of the link and a control ring, and fixing means for fixing a second end of the link on a pivot of a vane to be controlled, the device further comprising: a radial recess formed in the vane pivot for receiving the second end of the link, said recess having at least one plane edge inclined relative to a longitudinal midplane of the recess and co-operating with a corresponding inclined edge of the second end of the link; and a clamping cap bearing against the second end of the link and on which the fixing means act, said clamping cap having an inside surface providing plane contact with the outside face of the second end of the link against which said clamping cap bears in order to maintain the second end of the link against the vane pivot without slack by means of contact between said inclined edges.
As a result, the second end of the link is positioned without slack on the vane pivot by means of the inclined planes made in the radial recess and the second end of the link. The second end of the link is prevented from moving on the vane pivot by means of the clamping cap, and it is prevented from turning relative thereto by the fixing means. Thus, the precision of the turning drive imparted by the link to the vane pivot is improved.
A groove formed in the inside surface of the clamping cap and in which part of the second end of the link is engaged serves advantageously to prevent the clamping cap from turning relative to the other parts.
The radial recess formed in the vane pivot advantageously presents two inclined planes that are symmetrical about a longitudinal midplane of the recess so as to ensure that the link is held symmetrically on the vane pivot. The two inclined plane edges may also be asymmetrical about the midplane of the recess in order to provide keying distinguishing between a leading edge and a trailing edge of the link.